1. Field of the Invention
This invention relates to a warning light and more specifically to an aircraft anticollision warning light employing light emitting diodes as a light source.
2. Description of the Related Art
To prevent collisions, aircraft operating at night utilize a variety of lights to attract the attention of other aircraft operating in the same airspace. One such lighting system is the anticollision lighting system. A typical anticollision lighting system consists of flashing lights installed at several points on the aircraft to ensure that the lighted aircraft is visible to other aircraft operating in the vicinity. Anticollision lights are typically mounted on the aircraft's upper and lower fuselage, the tail, and the wingtips. Each of these anticollision lights is required to have a particular light radiation pattern. For example, the anticollision beacons mounted to the top and bottom of the aircraft are required to have a 360° radiation pattern in a horizontal plane. The radiation pattern has an intensity that is highest within an angle of 5° above and below the horizontal plane.
Anticollision lights have previously been installed on aircraft for this purpose, but they suffer from several disadvantages. Prior anticollision lights commonly use incandescent lamps and flashers or “rotating beacon” mechanisms to create an attention-getting pattern of light. However, flashers and rotating beacons suffer from limited life due to lamp burnout and mechanism wear. The amount of light emitted from these anticollision lights is also relatively low, affording limited attention-getting light at distances from the aircraft.
Many flashers and rotating beacon lights have been replaced by “strobe” lights owing to the strobe's brilliant, sharp flash and high light output. Strobe lights offer increased service life over flashers and rotating beacons due to the lack of incandescent lamps and moving parts. In a typical strobe lighting system, aircraft electrical power is converted to a high-voltage direct current (DC) potential. The high-voltage DC is applied to a xenon gas lamp, which is “triggered” to arc between its anode and cathode terminals by a second voltage which is applied to the lamp's grid terminal. Although more reliable than flashers and rotating beacons, strobe lights still suffer from a relatively short service life due to degradation of the strobe's electronic components from the continuous high-voltage charge and discharge cycles associated with each flash of the lamp. This charge/discharge cycle also tends to produce RF noise that is undesirable for aircraft components.
Light emitting diodes (“LEDs”) have previously been utilized for aircraft lighting, as shown in U.S. Pat. No. 6,203,180 to Fleischmann. However, Fleischmann teaches the use of light emitting diodes for interior cabin illumination, rather than exterior anticollision lighting, and does not address the attention-getting characteristics necessary for anticollision lights. U.S. Pat. No. 4,912,334 to Anderson discloses the use of light emitting diodes for anticollision lighting during covert aircraft operations. However, the requirements of anticollision lighting for covert and non-covert operations differ considerably. Covert operations require the use of infrared emitting diodes visible only to night vision imaging equipment. Further, the desired light output of covert anticollision lighting is of a comparatively low level and is intended to provide awareness only to other “friendly” aircraft operating in the immediate vicinity of the lighted aircraft. In contrast, the goal of non-covert visible-light anticollision lighting is to provide sufficient notice to other aircraft at distances from the lighted aircraft sufficient to avoid collisions by permitting emergency evasion procedures. There is a need for a strobe light that provides a sharp, bright pulse of visible light that can be seen at the significant distances desired for non-covert strobe anticollision lighting and which provides long operating life in the harsh aircraft environment.
U.S. Pat. No. 6,483,254 to Vo et al discloses an aircraft anticollision strobe light that employs LEDs arranged around the circumference of an electrically insulative, thermally conductive disc to form an LED light ring. Several LED light rings are stacked with electrically conductive rings placed between light rings. A control circuit applies current to the resulting stacked configuration. The '254 patent employs many densely packed LEDs to achieve the light intensity and radiation pattern required for an aircraft anticollision beacon. The massed LEDs of the '254 LED strobe light represent a typical, though inefficient use of LEDs as signaling light sources. The '254 LED strobe light is inefficient because a significant portion of the light produced by each LED is emitted in directions that do not reinforce the light emission from adjacent LEDs or the desired light radiation pattern. As a result, a great number of LEDs are required to meet the intensity standard for an aircraft anticollision beacon. Heat regulation always becomes a concern when using large numbers of closely packed LEDs. The configuration employed in the '254 patent is prone to overheating. Further, the '254 patent requires a power supply that provides current pulses sufficient to energize all of the LEDs in all of the rings to produce each desired light pulse. The requisite high amperage current requires a power supply with a robust design that is likely to increase costs. The high current power supply components will generate heat that must be dissipated to ensure reliable operation of the beacon. A further disadvantage is that a power supply necessary to generate the required high amperage current pulses may generate correspondingly large magnitude RF noise that may be difficult to filter.
There is a need in the art for an aircraft anticollision beacon that employs LEDs to efficiently meet the specified standard light intensity and radiation pattern for an anticollision beacon.